Image reproduction device screen



April 12, 1960 p, BUFF ETAL 2,932,570

IMAGE REPRODUCTION DEVICE SCREEN Filed Jan. 23, 1956 INVENTORS HUGH P. LA BUFF I OSEPH B. SHINAiL United States Patent IMAGE REPRODUCTION DEVICE SCREEN Hugh P. La Buff and Joseph B. Shinal, Seneca Falls, N .Y.,

assignors, by mesne assignments, to Sylvania Electric j Productslnc Wilmington, DeL, a corporation of Dela- W3 1 Application January 23, 1956, Serial No. 560,624

1 Claim. (CI. 96-45) This invention relates to image reproduction devices 2,932,570 Patented Apr. 12, 1960 ment utilizes a negative with a large number of parallel and more particularly to the preparation of viewing 1 screens for color television picture tubes.

One type of proposed television receiver for reproducingcolor television images employs an index type picture tube having a screen consisting of a series of parallel lines formed from fluorescent materials. The lines are arlines. The exposure time necessary to harden the photoresist to the degree required varies with the light intensity and exposure distance factors. A phosphor slurry 14 consisting of a photosensitive resist such as a mixture of polyvinyl alcohol, ammonium dichromate, ethyl alcohol, and water, and a phosphor such as zinc ortho-silicate, which fluoresces green, is next flowed over theexposed photosensitive film and dried. The dried surface is -then developed by washing with deionized water. The unexposed areas of the photosensitive film ranged so that an unmodulated scanning electron beam will excite the phosphors to produce a sequence of red, blue, and green fluorescence repeatedly across the screen in a manner well understood in the art.

The fluorescent screen conventionally is provided with a coating of an electron permeable film of aluminum. This fllm is deposited on the screen by flashing a pellet of aluminum onto a lacquer coating which had previously been deposited uponthe fluorescent materials by a floatation and decanting process. Indexing stripes are subsequently formed on the aluminum film to provide the secondary emissive indexing pulses necessary for the operation of a television receiver employing a picture tube of the type described above.

The indexing stripes are formed by a printing operation. Accordingly, the aluminum film is first covered by a lacquer coating, and a composition comprising polyvinyl alcohol, ammonium dichromate, ethyl alcohol and water is then deposited on the lacquer. The indexing pattern is formed by exposing this composition to ultra violet light through an appropriate negative. A slurry of the secondary emissive material, magnesium oxide, is subsequently flowed over the panel, and, after drying, the panel is developed with a water rinse.

In the manufacture of this type of television tube, many rejects occur which are due to the peeling or blistering of the aluminum film. It has been found that this blistering is very often caused by the presence of an undesirable amount of the alcohol used in the formation of the indexing stripes which dissolves the lacquer coating deposited on the back of the aluminum film.

Accordingly, one object of the invention is to reduce screen rejects caused by blistered aluminum coating.

Another object is the provision of an improved screen for color television picture tubes.

A still further object is the provision of an improved method for making cathode ray screens.

The foregoing objects are achieved in one aspect of the invention by the provision of a process of forming screens for a color television picture tube using a composition utilized in the formation of the indexing stripes which produce adequate indexing characteristics while reducing the number of screen rejects due to aluminum coating imperfections.

For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings in which Figs. 1 through 7 inclusive illustrate the steps involved in the formation of a coldr television picture tube screen.

In the drawings, a screen surface 10, which may be a clean dry glass face plate of a color picture tube, is

and the layer of slurry which adheres to those areas are washed away by the water while the exposed areas, which have been hardened, remain affixed to panel 10. The layer thus produced is air dried, after which the entire above described process is repeated for each of the remaining color emitting blue and red phosphors, with appropriate off-setting of the screen in relation to the master pattern for each successive color pattern. Zinc sulfide is the commonly used blue fluorescent phosphor while zinc phosphate may be employed as the red fluorescent phosphor. The resulting fluorescent pattern is shown in Figs. 1 and 2.

After the screen has been formed, a volume of water suflicient to cover the screen 14 is introduced into the bulb, and a thin coating of a nitrocellulose lacquer is subsequently floated on this water. As the water is decanted from the bulb, the lacquer adheres to the glass walls of the bulb and to the phosphor screen 14 so as to form a lacquer base 16. This lacquer coating is then dried and the inside of the bulb is coated under vacuum with an electron permeable substance 18 such as aluminum by a flashing technique to provide a screen as shown in Fig. 3. The excess aluminum is then removed from the side walls of the bulb.

The screened bulb is next baked in a lehr for approximately two hours at a temperature of approximately 425 degrees centigrade to remove any volatile impurities. During this bakeout operation, the nitrocellulose lacquer layer 16 shown in Fig. 3 also becomes volatile and is thus removed from the screen. The viewing panel crosssection then appears as shown in Fig. 4.

The indexing stripes are formed by first providing the aluminum with a back coating of nitrocellulose lacquer 20 which is applied in the same manner as the previous lacquer coating 16. Thereafter, a coating of the sensitized photoresist 22 is applied over the back lacquer 20, and dried. This photoresist 22 is exposed to ultra violet light through an appropriate negative to form a pattern of stripes, one of which is positioned over any one of the three phosphor color patterns. This photosensitive material consists of polyvinyl alcohol, water, ammonium dichromate, and ethyl alcohol. The polyvinyl alcohol and ammonium dichromate serve as the sensitized photoresist material needed in the photoprinting technique, While the ethyl alcohol is a foam killing agent in addition to a drying agent. It has been found that if the composition contains a. concentration of ethyl alcohol greater than 20 percent by Weight, it has a tendency to blister the aluminum film. This blistering is believed to be caused by the dissolution of an undesirable amount of the aluminum back coating of nitrocellulose lacquer in the ethyl alcohol. Experi ment has shown that a decrease in the concentration of the ethyl alcohol decreases the number of screen rejects. Elimination of ethyl alcohol in the indexing Grams Polyvinyl alcohol 2.3 Water 87.2 Ethyl alcohol 10.0 Ammonium dichro'mate .5

.After coating 22 has been applied to the panel, a secondary emissive composition comprising a magnesium oxide slurry is flowed onto the panel, and after drying, the pattern is developed by means of a demineralized water wash. This operation provides a pattern consisting of hardened photoresist 22 and the adhering secondary emissive material 24 as shown in Fig. 5. After drying, the bulb is again baked in a lehr to remove the lacquer 20 so that the screen appears as shown in Figs. 6 and 7.

While a particular embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claim.

4 What is claimed is: V In a process of making a screen for an image reproduction device wherein phosphor is afiixed to the panel; a metallic electron permeable film is deposited on the phosphor; a nitrocellulose lacquer layer is applied to the metallic film; a pattern of a composition comprising light sensitized polyvinyl alcohol and electron responsive secondary emissive magnesium oxide is formed on the lacquer film by light exposure of the polyvinyl alcohol through a pattern negative followed by development of the pattern by removal of the unexposed areas thereof; and the lacquer film is removed by volatilization thereof; the improvement comprising the application to said lacquer film during said composition pattern formation step prior to exposure, of an aqueous solution of said polyvinyl alcohol containing from 3 to 20 percent by weight of ethyl alcohol which controls foaming of said solution anddeleterious dissolution of said lacquer film.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Sylvania Technologist, July 1953, pages -63. 

1. IN A PROCESS OF MAKING A SCREEN FOR AN IMAGE REPRODUCTION DEVICE WHEREIN PHOSPHOR IS AFFIXED TO THE PANEL, A METALLIC ELECTRON PERMEABLE FILM IS DEPOSITED ON THE PHOSPHOR, A NITROCELLULOSE LACQUER LAYER IS APPLIED TO THE METALLIC FILM, A PATTERN OF A COMPOSITION COMPRISING LIGHT SENSITIZED POLYVINYL ALCOHOL AND ELECTRON RESPONSIVE SECONDARY EMISSIVE MAGNESIUM OXIDE IS FORMED ON THE LACQUER FILM BY LIGHT EXPOSURE OF THE POLYVINYL ALCOHOL THROUGH A PATTERN NEGATIVE FOLLOWED BY DEVELOPMENT OF THE PATTERN BY REMOVAL OF THE UNEXPOSED AREAS THEREOF, AND THE LACQUER FILM IS REMOVED BY VOLATILIZATION THEREOF, THE IMPROVEMENT COMPRISING THE APPLICATION TO SAID LACQUER FILM DURING SAID COMPOSITION PATTERN FORMATION STEP PRIOR TO EXPOSURE, OF AN AQUEOUS SOLUTION OF SAID POLYVINYL ALCOHOL CONTAINING FROM 3 TO 20 PERCENT BY WEIGHT OF ETHYL ALCOHOL WHICH CONTROLS FOAMING OF SAID SOLUTION AND DELETERIOUS DISSOLUTION OF SAID LACQUER FILM. 